Patent GB-1173511-A (GB)
Title: Improvements in or relating to Scanning of Cinematograph Film.
Inventor: CROWDER NORMAN ALLISON
IPC: H04N9/802
Filed: 1967-02-17
Abstract: 1,173,511. Television. COLUMBIA BROADCASTING SYSTEM Inc. 16 May, 1968 [17 Feb., 1967], No. 7804/67. Heading H4F. A video film reproducing apparatus comprises a flying-spot scanner arranged to scan a cinematograph film, which is moved at constant speed, with a raster of lines, in which a first periodic signal derived from a track on the film at a frequency equal to or a submultiple of the line frequency is compared in phase with a second periodic signal of the same frequency derived by means of a dividing circuit from a flywheel oscillator synchronized with and running at an even multiple of the frequency of the first periodic signal, the output of the comparator being sampled by the output of a cyclic counter stepped by pulses from the flywheel oscillator so that a frame pulse is provided the first time that the comparator output is sampled after a phase shift of 180 degrees in the first periodic signal. As shown, Fig. 1, the film 10 is scanned by a raster produced by a flying-spot scanner 18, the transmitted light being detected by a photomultiplier 24 to provide the video signal. A synchronization track 26 is illuminated by source 28 and the transmitted light is detected by a phototransistor 32. The synchronizing signal (a), Fig. 2, comprises a periodic waveform of half the line frequency and has a phase shift of 180 degrees eight lines before the end of the frame (or field). This signal is applied to a full-wave rectifier 34 to derive a signal (b), which is at line frequency and is unaffected by the 180 degree phase shift, which synchronizes a flywheel oscillator 36 controlling the line time base 20. The output (c) of the flywheel oscillator is halved in frequency by divider 40 to provide a signal (d) the phase of which is compared with signal (a) in comparator 42. During most of the frame (up to line 304) signals (a) and (d) are out of phase and the comparator output is zero but when signal (a) is shifted in phase by 180 degrees at line 304 the signals are in phase and the comparator output goes up. The output (c) of the flywheel oscillator is also applied to a counter 38 which produces an output after every eighth line as it resets. Since 304 is a multiple of 8 the counter is arranged to be reset at this line and next produces an output at line 312 which is applied to gate 44 together with the output of the comparator 42 which at this time is up so that a frame pulse (e) is produced which is used to synchronize the frame time base 22. The flyback pulse also triggers a monostable multivibrator 46 which during the blanking period inhibits gate 40 and also applies a signal to gate 48 so that after flywheel oscillator 36 has been pulled into step with the input signal an output pulse is produced if the output of divider 40 is in phase with the input signal to shift the phase of divider 40 by 180 degrees. Interlaced scans may be produced by providing the recorded synchronization signal (a) with a 90 degree phase shift at the end of the field, the blanking period being long enough for the flywheel oscillator to be pulled into the new phase. It is stated that in a colour system an R.F. subcarrier may be generated from the line frequency oscillator.